The objective of the proposal is to examine synaptic transmission in the cardiac ganglion of the frog and the mudpuppy (Necturus maculosus). The experiments have been designed to study what factors are involved in the maintenance of normal synapses, and in particular, what causes sprouting--the sudden renewed growth of intact mature nerve endings--when the ganglion is partially deafferented. The cardiac ganglion is a unique preparation in that it is very thin; when stretched out in a shallow chamber and viewed with a compound microscope, individual neurons, their processes, and synapses can be seen. Intracellular recordings with fine microelectrode will be used to investigate the electrophysiological activity in the ganglion cells and to study the phenomenon of sprouting. The studies seek to discover what causes the intact nerve terminals to sprout when some, but not all, of the preganglionic nerve fibers are destroyed, and to investigate whether the synapses formed by sprouting nerve fibers are functional and permanent. BIBLIOGRAPHIC REFERENCES: McMahan, U.J., S. Roper and D. Purves (1975). Acetylcholine sensitivity of multiply innervated autonomic neurons. 1975 Symposium on Quantitative Biology, Cold Spring Harbor, Abstract. Roper, S., D. Purves and U.J. McMahan (1975). Synaptic organization and acetylcholine sensitivity of multiply innervated autonomic ganglion cells. Cold Spring Harbor Symposium XL: In Press.